Infrared remote control (RC) systems are commonly used in a variety of electronic appliances to allow users to remotely control and/or program the appliances. One of the most widely used electronic appliances with an infrared RC system is a television. Using the infrared RC system, a user can remotely change various settings of the television, such as channel, audio volume, and picture control levels.
An infrared RC system of an electronic appliance includes an infrared transmitter and an infrared receiver. The transmitter is typically included in a handheld remote control, which allows a user to input the desired setting for the appliance. The transmitter modulates the outgoing infrared signal typically using amplitude shift keying (ASK) in response to the user input. The receiver is included in the appliance to receive and demodulate the modulated infrared signal so that the microcontroller in the appliance can change the setting of the appliance according to the user input.
A conventional infrared RC receiver for ASK modulated infrared signals includes a photodetector, an amplifier, a limiter, a bandpass filter, a demodulator, an integrator with a capacitor and a comparator with hysteresis. When an ASK modulated infrared signal is received, the photodetector produces an electrical signal in response to the infrared signal. The electrical signal is amplified by the amplifier, which is then limited by the limiter to ensure the amplified signal is within the input range of the bandpass filter. The bandpass filter selectively filters the signal based on frequency so that components of the signal within a particular frequency range is transmitted, while other components of the signal is attenuated. The bandpass filtered signal is then demodulated by the demodulator, the integrator and the comparator with hysteresis.
A concern with the conventional infrared RC receiver is that out-band noise is not effectively suppressed. Another concern with the conventional infrared RC receiver is that the integrator requires a significantly large capacitor, which introduces various disadvantages such as increased manufacturing cost and increased power consumption.
In view of these concerns, what is needed is a system and method for demodulating amplitude modulated optical signals with improved noise performance that can demodulate using a smaller capacitor than a conventional infrared RC receiver.